59

J Cardiol 2004 Feb; 43（2）: 59– 68

Relations Between Strength andEndurance of Leg Skeletal Muscleand Cardiopulmonary ExerciseTesting Parameters in Patients WithChronic Heart Failure

Kengo SUZUKI, MD

Kazuto OMIYA, MD

Sumio YAMADA, PhD＊1

Toru KOBAYASHI, PT＊2

Noriyuki SUZUKI, MD

Naohiko OSADA, MD

Fumihiko MIYAKE, MD,

─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────Objectives. The relations between muscle strength, muscle endurance, and cardiopulmonary parameters

were investigated in patients with chronic heart failure. Methods. The subjects comprised 33 outpatients with stable chronic heart failure（27 men, 6 women,

mean age 60.3±12.7 years）. A pedal-type isokinetic device was used throughout the study. The safety ofthe study protocol was examined first. Maximum muscle power（peak power）, an index of muscle strength,was measured for 6 consecutive revolutions（3 revolutions of each leg）. The strength decrement index（SDI）was measured for 20 consecutive maximal revolutions（10 revolutions in each leg）. The SDI is an index ofmuscle endurance and compares the mean power for revolutions 9 and 10 with that for revolutions 2 and 3.Each subjects underwent symptom-limited cardiopulmonary exercise testing with a cycle ergometer onanother day.

Results. No subject experienced continuous abnormal heart rate or blood pressure response, chest pain,ischemic ST-T change, or severe arrhythmia. The peak power and the SDI were correlated with the anaero-bic threshold（r＝0.42, 0.52, respectively）, with peak oxygen uptake（r＝0.66, 0.61）, and with theincrease in oxygen uptake per unit increase in work rate（r＝0.43, 0.63）. However, the slope of the venti-lation equivalent to carbon dioxide output was correlated only with the SDI（r＝－0.54）and the time con-stant for the oxygen uptake decrease was correlated only with the peak power（r＝－0.46）.

Conclusions. Peak functional capacity depends on both muscle strength and endurance, and subjectivesymptoms in daily activity, especially dyspnea on exertion, depend mainly on muscle endurance in patientswith chronic heart failure. ──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────J Cardiol 2004 Feb ; 43（2）: 59－68

Key WordsMuscle, skeletal Exercise tests Heart failure Ventilation

Abstract

──────────────────────────────────────────────聖マリアンナ医科大学 循環器内科 : 〒216－8511 川崎市宮前区菅生2－16－1 ; ＊1名古屋大学医学部 保健学科，名古屋 ; ＊2聖マリアンナ医科大学病院 リハビリテーション部，川崎Division of Cardiology, Department of Internal Medicine, St. Marianna University School of Medicine, Kawasaki ; ＊1School of HealthSciences, Nagoya University, School of Medicine, Nagoya ; ＊2Department of Rehabilitation Medicine, St. Marianna University Hospital,Kawasaki Address for correspondence : OMIYA K, MD, Division of Cardiology, Department of Internal Medicine, St. Marianna UniversitySchool of Medicine, Sugao 2－16－1, Miyamae-ku, Kawasaki 216－8511Manuscript received May 12, 2003 ; revised August 14 and October 8, 2003 ; accepted October 8, 2003PT＝physical therapist

INTRODUCTION

Many investigators have evaluated the effective-ness of exercise training in terms of functionalcapacity in patients with chronic heart failurewhose cardiac and skeletal muscle functions wereimpaired1－3）. However, even though a slightincrease in stroke volume with exercise training hasbeen observed, no improvement in myocardial con-tractility with exercise training has been found. Themuscle hypothesis4）suggests that the functionalimprovement after exercise training is not duemainly to a central effect such as cardiac perfor-mance but to peripheral effects such as adjustmentsof blood flow in skeletal muscle or of muscle func-tion. Considering the aging population of chronicheart failure patients, it is important to identify theskeletal muscle function that predominantly deter-mines functional capacity in the normal elderlypopulation.

There are several methods to evaluate skeletalmuscle functions, such as 31P-nuclear magnetic res-onance spectroscopy for evaluating aerobic meta-bolic competence5）, and near infrared spectroscopyfor evaluating the relative change in the state ofoxygenation and deoxygenation6）. However, thesemethods have disadvantages for repetitive measure-ments, such as the need for highly skilled operatorsand high cost. Therefore, isometric muscle strengthexpressed by peak joint torque has been used clini-cally as an index for skeletal muscle functionalcapacity7,8）, and no analysis of muscle endurancefor repetitive exercise has been done. The strengthdecrement index（SDI）, which was first reported byClarke et al 9）, can be used in isokinetic exercise asa simple measure of muscle endurance.

This study was designed to assess the relationsbetween several parameters measured in cardiopul-monary exercise testing, and muscle strength andendurance in terms of skeletal muscle function. Thesafety of measuring isokinetic muscle strength andmuscle endurance with the present equipment wasfirst evaluated because it had not been previouslydone.

SUBJECTS AND METHODS

SubjectsThis study included 33 chronic heart failure out-

patients（27 men and 6 women, mean age 60.3±12.7 years）who had typical symptoms and variousdegrees of left ventricular dysfunction from under-

lying cardiac disorders. They were all stable clini-cally and none had been hospitalized or had achange in medication during the previous three ormore months. Any subjects who met the EuropeanSociety of Cardiology criteria for exercise trainingcontraindications in patients with chronic heart fail-ure10）were excluded from the study. Patient charac-teristics are listed in Table 1.

The safety of our protocol was evaluated in 23 ofthe 33 patients（17 men, 6 women, mean age59.4±13.8 years）. The underlying diseases weredilated cardiomyopathy in 13 patients, previousmyocardial infarction in 7（4 anterior, 3 inferior）,and preoperative valvular heart disease in 3（1mitral stenosis, 1 mitral regurgitation, 1 aorticregurgitation）.

The study protocol was approved by theCommittee of Human Investigation of our

60 Suzuki, Omiya, Yamada et al

J Cardiol 2004 Feb; 43（2）: 59 – 68

Table 1　Characteristics of patients

Number of patients�

Mean age（yr）�

Male/female�

Etiology�

Dilated cardiomyopathy�

Old myocardial infarction�

Anterior�

Inferior�

Number of diseased vessels�

One-vessel disease�

Two-vessel disease�

Three-vessel disease�

Valvular heart disease�

Moderate AR�

Mild MS�

Severe MR�

Hypertensive heart disease�

Left ventricular ejection fraction（%）�

Brain natriuretic peptide（pg/ml）�

NYHA classification�

Medication�

Nitrates�

Calcium channel antagonists�

Angiotensin converting enzyme inhibitors�

AngiotensinⅡreceptor antagonists�

Beta blockers

33�

60.3±12.7�

27/6�

�

19�

9�

5�

4�

�

4�

4�

1�

4�

1�

1�

2�

1�

38.9±14.9�

174.7±166.3�

1.93±0.70�

�

5�

2�

14�

15�

9

Continuous values are mean±SD.�AR＝aortic valve regurgitation ; MS＝mitral valve stenosis ;�MR＝mitral valve regurgitation ; NYHA＝New York Heart Association.

University, and written informed consent wasobtained from each patient before participation inthe study.

Study equipmentA StrengthErgo240TM（SE240）pedal type isoki-

netic device（Mitsubishi Electric Corporation）wasused throughout this study（Fig. 1）. The measure-ment posture was a sitting position with backrest.The angle of the backrest was set at 110 degrees tothe horizontal plane. The position of the seat wasset to allow 30-degree knee flexion on leg exten-sion. The exercise started with the left leg at themaximal flexed knee position. The body and pelviswere fixed to the seat with a belt, and the subjectwas asked to grasp the grips at the side of the seatduring measurements. The pedal crank length wasadjusted to 172mm.

Measurements of muscle strength andendurance

To measure muscle strength, subjects were askedto pedal 6 consecutive revolutions（3 revolutionswith each leg）with maximal effort at 50 revolutionsper minute（rpm）after 5-minute rest（Fig. 2）. Threesets of measurements were made, with a 2-minuterest between sets. The torque generated at the ser-vomotor during pedaling was measured, and thework was calculated by multiplying the torque bypedaling time. The area enclosed by the parabolaand horizontal bar in Fig. 3 is a measure of musclepower. The maximum power（peak power）wasused as an index of muscle strength.

Following muscle strength measurements, mus-cle endurance was measured after a 10-minute rest.Subjects pedaled for 20 consecutive revolutions（10revolutions with each leg）at 60 rpm. The power at

Cardiopulmonary Parameters and Muscle Function 61

J Cardiol 2004 Feb; 43（2）: 59 – 68

Fig. 1 Photographs showing the complete pedal-type isokinetic device StrengthErgo240TM（SE240）a : Over view. b : The ankle joint is set to 90 degrees of flexion. c : Seat position is set to ensure a 30degree of knee flexion on leg extension. d : The angle of the backrest is set at 110 degrees to the horizontalplane.

Strength

Rest

5 min

HRBP

2 min 2 min 10 min 5 min

Strength Strength Endurance

Fig. 2 Schema of muscle strength and muscleendurance measurementsHR＝heart rate ; BP＝blood pressure.

the first revolution was ignored because the speedat the first revolution usually did not reach the tar-get speed. The SDI was calculated with theformula9）（Fig. 3）: SDI＝（S9-10）× 100/S2-3,where S9-10 is the mean power of the ninth and10th revolutions, and S2-3 is that of the second andthird revolutions. The SDI was calculated for eachleg, and the lower value was used for evaluation.The peak power was expressed as the value dividedby body weight（J/kg）, and muscle endurance wasexpressed as the SDI（%）. Preliminary experimentsfound that the SDI at 60 rpm was significantlylower than that at 50 rpm in patients with heart fail-ure and that differences in the SDI are moredemonstrable at 60 rpm.

Single-lead electrocardiographic monitoring wascontinued throughout the muscle strength andendurance measurements. Blood pressure was mea-sured before, immediately after, and 1.5 min afterstrength measurements ; and immediately after, 3,and 5 min after the endurance measurements. Therate pressure product was calculated as the productof heart rate and systolic blood pressure. Patientswere asked to assign a rating to their perceivedexertions of the chest and legs separately on a 6 to20 category scale11）during the measurements.

The criteria for terminating both the musclestrength and endurance tests were development ofchest pain, severe dyspnea, severe fatigue, sus-

tained blood pressure drop, sustained ventriculartachycardia, short runs of three or more ventricularpremature contractions, pallor, and dizziness.

Cardiopulmonary exercise testingTwo muscle function tests and a cardiopul-

monary exercise test were carried out on differentdays within 2 weeks. The cardiopulmonary exercisetest was performed on a CORIVAL 400 sittingcycle ergometer（LODE B.V.）with a ramp exerciseprotocol. Exercise load intensity was increasedgradually and linearly by 1 W per 6 sec after a 3-minute rest and 4-minute warm-up stage of 0 or20 W. Heart rate response, ST-T changes, andarrhythmias during the exercise test were moni-tored continuously with a ML-5000 stress test sys-tem（Fukuda Denshi Co.）, and standard 12-leadelectrocardiography was performed every minute.Blood pressure was also recorded with a STBP-780automated sphygmomanometer（Colin Co.）everyminute.

The criteria for halting exercise testing in thisstudy were according to the guidelines of theAmerican College of Sports Medicine12）. Theexpired gas was analyzed in the sitting positioncontinuously for 5 min of a recovery phase withoutcool-down exercise to measure the time constant ofthe oxygen uptake（・VO2）decrease in the earlyrecovery phase（τoff）.

62 Suzuki, Omiya, Yamada et al

J Cardiol 2004 Feb; 43（2）: 59 – 68

Power（J） Torque（Nm） 500

400

300

200

100

0

150Left leg Right leg

100

50

01 109876

Pedal revolutions Angle of pedal（degree）

5432180 360

Fig. 3 Schema of strength decrement index measurementLeft : Isokinetic muscle power（J）decreases gradually from the first to 10th revolutions（Black bars : Leftleg. White bars : Right leg）.Right : Isokinetic muscle power is the area enclosed by the parabola and the horizontal bar. Power decreas-es gradually with each revolution. Strength decrement index（%）is calculated from the mean power valueobtained from the second and third and the ninth and 10th revolutions.

Expired gas analysis was performed throughouttesting using a breath-by-breath basis with an AE-280 cart（Minato Medical Science）. The quantitiesderived from cardiopulmonary exercise testingwere anaerobic threshold, peak oxygen uptake（peak・VO2）, slope of the ventilatory equivalent tocarbon dioxide output（・VCO2）［・VE/・VCO2 slope］,and the change in ・VO2 relative to change in workrate（WR）［Δ・VO2/ΔWR］. ・VE/・VCO2 slope andτoff were calculated with accessory software onthe AE-280.

Statistical analysisAll values are expressed as mean± standard

deviation. Comparison of two parameters usedStudent’s t-test, and analysis of the correlation oftwo parameters used Spearman’s single regression.The statistical significance level of measurementswas set at less than 5%.

RESULTS

Evaluation of safety in measuring musclestrength and muscle endurance

All subjects completed the protocol withoutcomplications. No subject complained of chestsymptoms, such as chest pain, chest oppression, orshortness of breath, during the test period. Ratingsof perceived exertion during muscle strength mea-surements ranged from 9 to 16（mean 12.3±1.5for the chest, 12.5±1.5 for the legs）; and duringendurance measurements, ratings of perceivedexertion ranged from 11 to 17（mean 13.5±1.5 forthe chest, 13.2±1.7 for the legs）.

Heart rate and blood pressure responses aregiven in Table 2. A transient decrease in systolicblood pressure from baseline occured in nine sub-jects immediately after the measurement of eithermuscle strength or muscle endurance（mean 7.9±3.1 mmHg）. Three of the nine subjects had chronicatrial fibrillation. None of the nine subjects hadchest pain or ischemic ST-T changes. Systolic

blood pressure in these subjects recovered within1.5 min after the measurements. The systolic bloodpressures in Table 2 were measured after recoveryfrom blood pressure decreases.

Chronic atrial fibrillation was present in 5 of 23subjects. Monofocal ventricular premature contrac-tions appeared after the measurements in 10 sub-jects, and monofocal atrial premature contractionsappeared after the measurements in 4 others.Ventricular couplet beats appeared in one subject.No subject had short runs of three or more ventricu-lar premature contractions or ischemic electrocar-diogram（ECG）changes after the examination.

Relations between muscle strength andendurance and parameters measured by car-diopulmonary exercise tests

The peak power was 13.4±3.1 J/kg（Fig. 4）andthe SDI was 85.1±4.8%（Fig. 5）. The parametersmeasured by cardiopulmonary exercise tests wereanaerobic threshold 14.8± 2.8 ml/min/kg ;peak・VO2 21.6± 5.7 ml/min/kg ; ・VE/・VCO2 slope32.8±6.8 ; Δ・VO2/ΔWR 9.8±2.5 ml/W ; τoff62.5±14.6 sec.

Both the peak power and the SDI had significantcorrelations with the anaerobic threshold（r＝0.42,0.52, respectively）, peak・VO2（r＝ 0.66, 0.61）,Δ・VO2/ΔWR（r＝ 0.43, 0.63）. However, the・VE/・VCO2 slope was correlated only with the SDI（r＝－0.54）, andτoff was correlated only withthe peak power（r＝－0.46）.

DISCUSSION

Safety of isokinetic muscle power and muscleendurance measurement

Recently, resistance training has been consideredsafe for cardiac patients, especially patients withischemic heart disease or patients after coronaryartery bypass surgery, because this type of trainingleads to an increase in diastolic blood pressure thatcontributes to an increase in coronary blood flow

Cardiopulmonary Parameters and Muscle Function 63

J Cardiol 2004 Feb; 43（2）: 59 – 68

Table 2　Heart rate, blood pressure and rate pressure product changes during measurements

Heart rate（beats/min）�

Systolic blood pressure（mmHg）�

Diastolic blood pressure（mmHg）�

Rate pressure product（×102）�

76.9±9.5 �

123.0±18.8 �

71.7±12.3�

93.4±16.4

Rest

100.0±18.1 �

128.6±19.5 �

72.5±10.3�

129.4±37.8

First strength

104.0±21.3 �

128.8±20.3 �

73.8±9.6 �

134.3±38.3

Second strength

102.9±18.7 �

129.8±21.0 �

72.9±11.0�

134.4±38.0

Third strength

119.9±28.4 �

136.3±21.6 �

73.5±10.9�

165.9±59.5

Endurance

Values are mean±SD.

without a major increase in heart rate13）. The fewreports of resistance training or testing in patientswith chronic heart failure indicated that in patientswith heart failure in New York Heart Association（NYHA）classⅠ toⅢ and mean left ventricular

ejection fraction of 35%14）, no significant differ-ences were found in heart rate and blood pressureresponses between the resistance training and step-wise recruitment load exercise tests. The load dur-ing isokinetic muscle power and endurance mea-surements was relatively low because peak heartrate and peak systolic blood pressure in the presentstudy were much lower than peak values obtainedfrom cardiopulmonary exercise testing.

Although several subjects had a transient bloodpressure decrease, the cause is uncertain, but mayhave been due to delayed autoregulation of myocar-dial blood flow15）. A single-formula exercise load-

ing and suddenly strenuous exercise test withoutany warm-up stage caused a lower heart rate, bloodpressure, rate pressure product, and left ventricularejection fraction than the same protocol with awarm-up stage in healthy subjects15）. The differ-ence was explained by delayed autoregulation ofmyocardial blood flow, leading to low left ventricu-lar ejection fraction and subendocardial ischemia inthe sudden strenuous exercise test without warm-up. The blood pressure decreases were acceptablebecause of the very short duration and absence ofECG changes or severe arrhythmias.

Although the increases in blood pressure, heartrate, and rate-pressure product from rest to the endof the measurement of muscle endurance werehigher than those in the strength measurements, nosubject experienced severe arrhythmia or ischemicECG change. Moreover, patient symptoms accord-

64 Suzuki, Omiya, Yamada et al

J Cardiol 2004 Feb; 43（2）: 59 – 68

Peak power （J/kg）

25

20

15

10

5

0

25

20

15

10

5

0

25

20

15

10

5

0

0 10

AT（ml/min/kg）

ΔVO2/ΔWR τ off（sec）

Peak VO2（ml/min/kg） VE/VCO2 slope

20

5 10 15 20 30 40 50 60 70 80 90 100

25

20

15

10

5

0

25

20

15

10

5

00 3020 40 0 3020 40 50 60

r＝0.42 p＝0.0124

r＝0.43 p＝0.0128

r＝－0.46 p＝0.0076

Peak power （J/kg）

Peak power （J/kg）

Peak power （J/kg）

Peak power （J/kg）

r＝0.66 p＜0.0001

r＝－0.32 p＝0.0620

・

・

・ ・

Fig. 4 Correlations between peak power and cardiopulmonary exercise parametersPositive correlations are observed between peak power and AT, peak・VO2 andΔ・VO2/ΔWR. A negativecorrelation is recognized between peak power andτoff. No correlation is seen between peak power andthe・VE/・VCO2 slope.AT＝anaerobic threshold ; ・VO2＝oxygen uptake ; ・VE/・VCO2 slope＝ slope of the ventilation equivalent tocarbon dioxide output ; Δ・VO2/ΔWR＝change in・VO2 relative to change in work rate ; τoff＝ time con-stant for post-exercise・VO2 decrease.

ing to the ratings of perceived exertion were rela-tively mild. In general, the isokinetic exercise modeis thought to be relatively safe for cardiac patientsbecause the load does not exceed the preset loadand pedaling speed is regulated.

Relations between muscle power and muscleendurance and parameters measured by car-diopulmonary exercise testing

Resistance training does not achieve a significantimprovement in peak・VO2 in normal subjects16,17）,but a significant correlation was found betweenskeletal muscle volume and peak・VO2 in patientswith chronic heart failure18）. These findings suggestthat isokinetic muscle power is related to skeletalmuscle volume, which is associated with peak・VO2

in patients with chronic heart failure. We found thatpeak・VO2 correlated with both muscle strength andendurance. The subjects in the present study hadonly mild heart failure, so possibly had not sufferedskeletal muscle atrophy.

Theτoff in the early recovery phase reflects thedegree of oxygen debt or exercise intensity, andincreases with the severity of cardiacdysfunction19）. Theτoff has close negative corre-lations with anaerobic threshold, peak・VO2, andΔ・VO2/ΔWR in patients with left ventricular dys-function20）. Therefore, τoff may be a better pre-dictor of hemodynamic abnormalities in cardiacdiseases. We inferred that improvement of musclestrength might contribute to improved peak・VO2

and reducedτ off because isokinetic musclestrength was correlated significantly withτoff. Wesuggest that improvement of isokinetic musclestrength is associated with improvement of musclevolume, which contributes to an increase in venousreturn and cardiac output during exercise.

The・VE/・VCO2 slope increases with the severity ofheart failure and the level of dead space ventilation,so is a useful index for dyspnea during exercise21）

and a strong predictor of mortality in patients withchronic heart failure22）. A study of the relation

Cardiopulmonary Parameters and Muscle Function 65

J Cardiol 2004 Feb; 43（2）: 59 – 68

SDI（％）

r＝0.52 p＝0.0015

r＝－0.37 p＝0.0413

r＝0.63 p＜0.0001

100

90

80

70

100

90

80

704 6 8 10 12 14 16

10 15 20 1070

80

90

100

70

80

90

100

20 30 40

2070

80

90

100

40 60 80 90

SDI（％） SDI（％）

AT（ml/min/kg）

ΔVO2/ΔWR τ off（sec）

Peak VO2（ml/min/kg） VE/VCO2 slope

30 3520 25 40 45 50 55

r＝0.61 p＜0.0001

r＝－0.54 p＝0.0007

・

・

・ ・

Fig. 5 Correlations between the strength decrement index and cardiopulmonary exercise parame-tersPositive correlations are observed between the strength decrement index and AT, peak・VO2, andΔ・VO2/ΔWR. A negative correlation is noted between the SDI and the・VE/・VCO2 slope. No correlation is seenbetween the strength decrement index andτoff.SDI＝ strength decrement index. Other abbreviations as in Fig. 4.

between functional capacity and isokinetic musclestrength found that muscle strength had a signifi-cant negative correlation with the・VE/・VCO2 slopebut not with peak ・VO2

7）. Our findings that muscleendurance had a significant correlation with the・VE/・VCO2 slope and that muscle strength was notcorrelated with the・VE/・VCO2 slope differ from theprevious findings7）. The subjects in the previousstudy comprised 10 patients with chronic heart fail-ure patients and 10 healthy controls who had verygood values of peak・VO2 and muscle peak torque.The・VE/・VCO2 slope may be correlated more closelywith muscle power in normal subjects than in heartfailure patients.

Both dyspnea and the・VE/・VCO2 slope wereimproved in patients with chronic heart failure afteraerobic exercise training and low-level leg resis-tance training23）. The peripheral muscle might bethe location of the key transducer for the sensationsof dyspnea and fatigue in cardiac patients ratherthan cardiac function. Our finding of a close corre-lation between muscle endurance and the・VE/・VCO2

slope supports this hypothesis.In patients with chronic heart failure, the blood

supply to active skeletal muscle decreases due tolow cardiac output, and oxygen utilization in activeskeletal muscle is increased. As a result, the arteri-ovenous oxygen difference increases and compen-satory blood flow redistribution occurs to increaseoxygen transport to active skeletal muscle.Therefore, lowΔ・VO2/ΔWR in patients withchronic heart failure implied low oxygen consump-tion at a constant workload. In our study,Δ・VO2/ΔWR was correlated with muscle endurance ratherthan with isokinetic muscle strength. This resultsuggests that muscle endurance, which is the abilityto continue muscle activity under a constant work-load, is associated with adequate oxygen transport

to peripheral tissue.

Study limitationsThe subject population was small and inhomoge-

neous. Moreover, all patients had mild heart failure（mean NYHA classification was 1.93± 0.7）.These subjects may not have suffered any markeddecrease in muscle strength, muscle endurance, andfunctional capacity. Thus, further investigation ofpatients with more severe heart failure is needed.

Clinical implicationsThe SDI had close correlations with both anaero-

bic threshold and the・VE/・VCO2 slope, which areconsidered to be related to the quality of dailyactivity including dyspnea on exertion. Training toincrease muscle endurance and muscle strengthshould be encouraged to improve the quality of lifeor dyspnea in patients with chronic heart failure. Atraining program for increasing muscle endurancemay be developed with the equipment and the pro-tocol used in this study.

CONCLUSIONS

Isokinetic muscle strength and endurance mea-surements can be made safely in patients with sta-ble chronic heart failure. The peak・VO2 in patientswith chronic heart failure is correlated with bothmuscle strength and endurance, whereas subjectivesymptoms in daily activity including dyspnea arecorrelated mainly with muscle endurance.

Acknowledgements

We wish to thank S. Watanabe, PT, K. Izawa, PT, and the cardiac

rehabilitation staff in the Department of Rehabilitation Medicine, St.

Marianna University Hospital, for their technical assistance in this

study.

66 Suzuki, Omiya, Yamada et al

J Cardiol 2004 Feb; 43（2）: 59 – 68

Cardiopulmonary Parameters and Muscle Function 67

J Cardiol 2004 Feb; 43（2）: 59 – 68

慢性心不全患者における下肢骨格筋力 筋持久力と

心肺運動負荷試験諸指標との関連

鈴木　健吾　　大宮　一人　　山田　純生　　小 林　 亨

鈴木　規之　　長田　尚彦　　三宅　良彦

目　的 : 慢性心不全患者の運動耐容能を規定する因子として，下肢骨格筋の重要性が報告されているが，心肺運動負荷試験における指標との具体的な関連を検討した報告は少ない．本検討は，慢性心不全患者の下肢の筋力，ならびに筋持久力と呼気ガス分析諸指標との関連を明らかにすることを目的とした.

方　法 : 対象は，状態の安定した慢性心不全患者 33例（男性 27例，女性 6例，平均年齢 60.3±12.7歳）である．ペダル駆動型等速性筋力測定装置を用い，初めに本プロトコルの安全性を検討した．6回連続ペダル駆動（各脚3回）における最高仕事量（最高パワー）を筋力の指標，また20回連続駆動（各脚10回）における仕事量の減衰率を strength decrement index（SDI）とし，筋持久力の指標とした．SDIは9および10回転目のパワーの平均と2および3回転目のパワーの平均から求めた．また，別の日に自転車エルゴメーターを用いた症候限界性心肺運動負荷試験を行った．結　果 : 本プロトコル中に心拍数，血圧の過度の反応はなく，胸痛やST-T異常，重症不整脈も

出現しなかった．最高パワーおよびSDIはいずれも，嫌気性代謝閾値（それぞれ r＝0.42，r＝0.52），最高酸素摂取量（r＝0.66，r＝0.61）および仕事率の増加量に対する酸素摂取量の増加量（r＝0.43，r＝0.63）と有意な相関を有した．しかしながら，二酸化炭素排出量に対する換気当量の傾きはSDI

のみと（r＝－0.54），運動後酸素摂取量減衰時定数（r＝－0.46）は最高パワーのみと相関した．結　論 : 慢性心不全患者の最高身体能力は筋力および筋持久力の両者に依存しており，これに対

して日常生活における自覚症状，とくに労作時の呼吸困難感は主に筋持久力に依存していると考えられた．

J Cardiol 2004 Feb; 43（2）: 59－68

要　　　約

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